This invention relates to a timing control device in which the position of a moving body which runs at a given speed is detected, and according to the detection signal, a signal for starting an operation with a predetermined delay time is produced.
More specifically, the invention relates to a timing control device in which the position of a moving body such as a print band or a print hammer of a printer, which runs at a given speed, is detected, so that the print hammer is driven at the exact time instant whereby characters are printed correctly.
A printer will be described, by way of example, in which a plurality of print hammers 1 having dot elements are arranged in parallel with the print line, and a hammer bank 2 supporting these print hammers 1 is reciprocated across the printing paper, so that during reciprocation the print hammers 1 are selectively operated to print dots at selected positions (FIG. 1).
The printer has thirty-four print hammers 1, each of which is reciprocated over a distance corresponding to four characters. A cam device is employed to reciprocate the hammer bank 2. An encoder disc 5 for detecting the positions of the print hammers 1 and a pulley 6 for transmitting the power of a motor 9 are mounted on the cam shaft 4 of the cam device 3.
As the motor 9 rotates, the pulley 6 is turned through a pulley mounted on the output shaft of the motor 9 and a timing belt 7, so that the hammer bank 2 is reciprocated by means of the cam device 3. The locus of motion of the hammer bank 2 is as shown in FIG. 2.
Slits 10 are formed in the encoder disc 5 in correspondence to print positions on the locus of motion in FIG. 2. A detector 12 is provided to detect the slits 10. More specifically, when the detector 12 detects a slit 10, it outputs a logical value "1"; and when the detector 12 detects no slit 10, it outputs a logical value "0".
In order to detect the direction of reciprocation of the hammer bank 2, an additional slit 11 distinct from the aforementioned slits 10 is formed in the encoder disc 5. The slit 11 is detected by detectors 13 and 14. More specifically, the hammer bank 2 is moved from left to right for the time interval which elapses from the instant when the detector 13 detects the slit 11 to provide a logical value "1" until the detector 14 detects the slit 11 to output a logical value "1". On the other hand, the hammer bank 2 is moved from right to left for the time interval which elapses from the instant the detector 14 detects the slit 11 to output a logical value "1" until the detector 14 detects the slit 11 to provide the logical value "1".
In order to print dots at the print positions on the locus of motion shown in FIG. 2, the time instant when the slit 10 corresponding to each print position is detected by the detector 12 should be advanced by the flight time T.sub.f which elapses from the instant the print hammer 1 is driven until it strikes against the printing paper. This may be achieved by employing a method in which adjustment is accomplished by displacing the detector 12.
The locus of motion of the hammer bank 2 is defined by the cam device 3; however, in positioning the cam and the encoder disc 5, it is difficult to position them accurately at the reference position; in other words an error of .+-.5 degrees, in general, takes place. Accordingly, the range of adjustment of the detector 12 is more than .+-.5 degrees with respect to the detector mounting reference position.
On the other hand, in the printer, four characters are printed by one hammer 1. One character is composed of tweleve dots. Accordingly, the hammer has 48 dot print positions in the lateral direction. When the cam of the cam device 3 makes one revolution, the hammer bank 2 accomplishes one reciprocation. That is, when the encoder disc 5 turns through 180 degrees, the hammer bank 2 accomplishes a one-way motion. During this period, dots must be printed at 48 dot print positions, and the printing paper must be advanced vertically to the next dot position. The time required for advancing the printing paper converts into an angle of rotation of about 50 degrees of the encoder disc 5. Thus, 48 slits 10 are distributed within an angle of about 130 degrees; that is, the slits 10 are provided at angular intervals of about 2.8 degrees. Accordingly, three of four slits 10 are provided within an adjustment range of .+-.5 degrees, i.e. in the range of 10 degrees.
As it is difficult to adjust the mechanism, a method of electrically varying the print hammer drive time has been employed in such a printer.
In this method, when the detector 12 detects the slit 10 in the encoder disc 5 and outputs the logical value "1", a monostable multivibrator is operated, and an output signal provided when the multivibrator is stopped is employed as the print hammer drive start time. The same effect as that which is obtained by adjusting the mechanism is obtained by varying the output time of the multivibrator.
The method may be employed in the case where the variable time width of the multivibrator is smaller than the value obtained by converting the angular interval of the slits 10 into time; however, it is not employable in the case where the former is larger than the latter, because the positional correspondence is shifted.
That is, the above method is not employable in the case where the range of adjustment is wide, as just described; that is, in the case where three of four slits 10 are included in the range of adjustment.